`AssetTxFeePaid` event should return fee and tip amounts in the asset ID

[IkerAlus]

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• This is not a support question.

Description of bug

When an AssetTxFeePaid event of the asset-tx-payment pallet is emitted, the fees and tip are subtracted from the asset ID balance of the sending account. However this event currently returns the tip and actualFee fields in balances of the chain native token. This is confusing for users and external tools, since they assume the values displayed in those fields are given in units of the asset ID.

Steps to reproduce

Example screenshot of a transaction on Statemint paying the fees in the asset ID 1984 but emitting the AssetTxFeePaid event in DOT balances:

[Szegoo]

I think this is a reasonable change(I am not the one to make the decision here though). If this gets confirmed I will open a simple PR for this.

[bkchr]

Sounds reasonable as well to me! Please open a pr @Szegoo

[Szegoo]

I realised that this is not as easy and simple to implement as I thought :P
This would require us to make the BalanceOf<T> generic inside the transaction-payment pallet.
We could do something like this:

pub fn compute_actual_fee<Balance: FixedPointOperand + AtLeast32BitUnsigned>(

So when we make a call to this from the asset-tx-payment pallet we would call this like the following:

let actual_fee = pallet_transaction_payment::Pallet::<T>::compute_actual_fee::<AssetBalanceOf<T>>(
	len as u32, info, post_info, tip,
);

This way we could make the Balance type generic but this does complicate the code a bit and also results in less readable code.

I think the person who originally wrote the code was aware of this compromise and decided that it was not worth it.

I am curious what you think about this @bkchr.

[bkchr]

Not sure I can follow you, don't we just need to add a BalanceToAsset: BalanceConversion<BalanceOf<Self>, AssetIdOf<Self>, AssetBalanceOf<Self>> to the Config trait of asset-tx-payment and then call this code:

substrate/frame/transaction-payment/asset-tx-payment/src/payment.rs

Lines 153 to 155 in ea387c6

	let converted_fee = CON::to_asset_balance(corrected_fee, paid.asset())
	.map_err(|_| -> TransactionValidityError { InvalidTransaction::Payment.into() })?
	.max(min_converted_fee);

to convert the balance fee to the asset balance fee?

[Szegoo]

Correct, I overlooked that and started complicating 😅